AN X-RAY REFLECTIVITY STUDY OF MONOLAYERS AND BILAYERS OF ARCHAE LIPIDS ON A SOLID SUBSTRATE

Membranes of archaebacteria show some very interesting features, the m ost prominent being their stability at high temperatures. This propert y seems to be caused by the bipolar nature of the membrane lipids. The configuration of the lipid molecules in a monolayer of a native mixtu re of lipids extracted from Sulfolobus solfataricus has been studied b y X-ray reflectivity of samples on solid substrates. Films on substrat e were prepared by Langmuir-Blodgett techniques. We used both pure sil icon (hydrophilic) and silicon covered by dimethyldichlorosilane, rend ering the surface hydrophobic. Data were analysed using a box-model an d the recursion scheme of Parratt. The results for the samples on hydr ophobic substrate are interpreted by a stretched horizontal configurat ion. The electron densities and thickness of the layers are in good ag reement with a model of close-packed molecules lying flat on the surfa ce. Samples on pure silicon show a U-shape form of the molecules. (C) 1998 Published by Elsevier Science S.A. All rights reserved.